1. Field of the Invention
The present invention relates to a binder resin for an electrophotographic toner and a toner containing the same.
2. Description of the Prior Art
In an electrophotography, the method of applying a heat roller has been widely used to fix an electrostatic latent image visualized with a toner. In applying this method, it is required that the lowest fixing temperature of the toner (Tf; the lowest heat roller temperature when 70% of the fixing strength is obtained) is sufficiently low and the hot offsett temperature (Th; the lowest heat roller temperature when the hot offset is observed) is sufficiently high.
In order to satisfy these two requirements, there have been done many proposals previously on the toner binder resin having a wide range of molecular weight distribution ranging from low molecular weight to high, for example, U.S. Pat. No. 3,941,898. According to these proposals, the molecular weight distribution is spreaded to upperside by using a crosslinking agent or the like.
When the molecular weight distribution is spreaded to upper side by using a crosslinking agent as mentioned in the above, however, there occurs a defect of arising high Tf.
On the other hand, such method may be also available as preparing a high molecular weight portion by a dispersion polymerization, and then mixing and solving it in a solvent with a low molecular weight polymer prepared separately. According to this method, however, when the molecular weight gap of these polymers is large, colorants such as carbon black and additives such as a charge controlling agent cannot be dispersed uniformly, that the charging property in the copy running is unstable, and that the blushing or the scattering of the toner occurs.
It is one of the object of the present invention to obtain, by solving the above-mentioned problems, a binder resin for an electrophotographic toner available for supplying low Tf together with high Th.
Another object of the invention is to obtain a binder resin for an electrophotographic toner providing a toner having a property of dispersing colorants such as carbon black and additives such as a charge controlling agent uniformly in the preparation of the toner, and giving an excellent copy running property. Still another object of the invention is to obtain an electrophotographic toner containing said binder resin.
These and other objects of the invention will become more readily apparent from the description hereinafter.